Fears over the potential for multibillion-pound fines and damages from the industry's rate-rigging scandal have sent banks' shares tumbling.
Barclays plunged as much as 17%, wiping about £4 billion from its market value, as concerns mounted that the £290 million fines imposed on the bank could be dwarfed by the cost of lawsuits.
The shockwaves were felt throughout the sector as speculation suggested the interbank lending rate scandal was set to engulf other British banks.
Royal Bank of Scotland dropped 12%, Lloyds Banking Group fell 7% and HSBC was 4% lower.
Sandy Chen, banking analyst at Cenkos Securities, said he was braced for billions of pounds in fines and damages across the sector.
He said: "The cost of lawsuits related to the Libor rate scandal will likely dwarf the £290 million fine imposed on Barclays - and since Royal Bank of Scotland, HSBC and Lloyds Banking Group have also been named in lawsuits, we expect they will also face significant fines and damages. We are pencilling in multi-year provisions that could run into the billions."
Mr Chen said recent disclosures on interest rate derivatives gave an indication of each bank's potential exposure to the rate scandal.
RBS reported £422 billion, HSBC reported 513 billion US dollars (£328 billion) and Lloyds recorded £43 billion, according to Mr Chen.
Analysts at Killik & Co agreed the interbank probe was likely to pull in other UK banks, but said Barclays should be able to withstand multibillion-pound damages.
They said: "Some estimates are that potential damages could run into the several billions of dollars, certainly damaging to Barclays but not too significant in the context of core tier one capital of £43 billion and annual net income over £3 billion."